Imaging system

ABSTRACT

1. IN AN IMAGING METHOD WHEREIN A COHESIVELY WEAK PHOTORESPONSIVE IMAGING LAYER COMPRISING ELECTRICALLY PHOTOSENSITIVE PARTICLES DISPERSED IN AN INSULATING BINDER IS SANDWICHED BETWEEN TWO SHEETS, THEN EXPOSED TO A PATTERN OF ACTINIC ELECTROMAGNETIC RADIATION AND AN ELECTRIC FIELD THEREBY PROVIDING UPON SEPARATION OF THE SHEETS A POSITIVE IMAGE ON ONE SHEET AND A NEGATIVE IMAGE ON THE OTHER, THE IMPROVEMENT COMPRISING: TREATING THE ELECTRICALLY PHOTOSENSITIVE PARTICLES WITH FROM ABOUT 20% TO ABOUT 200% BY WEIGHT OF SAID PARTICLES OF A MATERIAL SELECTED FROM THE GROUP CONSISTING OF POLYISOBUTENYLSUCCINIC ANHYDRIDE AND POLYISOBUTENYLSUCCINIC ANHYDRIDE DERIVATIVES PRIOR TO FORMATION OF SAID IMAGES.

Nov. 5, 1974 G J, REINIS &846.127

IMAGING SYSTEM Filed Aug. 30, 1972 HILL JI H *United States Patent Oflice 3,846,127 Patented Nov. 5, 1974 3,846,127 IMAGING SYSTEM Gedeminas J. Reinis, Rochester, N.Y., assignor to Xerox Corporation, Stamford, Conn. Filed Aug. 30, 1972, Ser. No. 284,817 Int. Cl. G03c 5/10 U.S. Cl. 96--1 M 23 Claims ABSTRACT OF THE DISCLOSURE In an imaging system wherein a cohesvely weak photoresponsive imaging layer comprisng photosensitive pigment particles dispersed in an insulating binder is sandwiched between two sheets, then exposed to a pattern of actinic electromagnetic radiation and an electric field thereby providing upon separation of the sheets a positive image on one sheet and a negative image on the other, the electrcally photosensitive pigment particles are treated with polyisobutenylsuccinic anhydride or derivatives thereof before being incorporated in the imaging layer thus resulting in improved images.

BACKGROUND OF THE INVENTION The present invention relates in general to imaging and more specifically to an imaging method for the formation of images by imaging layer transfer in image configuration as well as the imaging materials used theren.

Manifold imaging, a technique based on layer transfer of a colored material in image configuration is described in detail in copending application Ser. No. 708,380, filed Feb. 26, 1968, and incorporated by reference herein. Generally speaking, manifold imaging utilizes a structure comprising an electrcally photosensitive cohesvely weak (or field fracturable) imaging layer sandwiched between a donor sheet and a receiving sheet. An electric field is imposed across the imaging layer and the imaging layer is exposed to irnagewise actinic radiation. Upon separation of the donor and receiver sheets the imaging layer fractures in imagewise configuration corresponding to the imagewise exposure with an image which is positive in image sense adhering to one of the sheets and an image which is negative in image sense adhering to the other sheet. Although imaging layers may be prepared which are themselves cohesvely weak or field fracturable to respond to the application of light and electric field, a larger range of materials may be used if an activating" step is included in the process. The activating step serves to structurally weaken the imaging layer so that it can be more easily fractured along a sharp line which defines the image to be reproduced. Conventionally the imaging layer is activated by treating it with a swelling agent or a partial solvent for the material prior to placing the imaging layer between the donor and the receiver sheets. Alternatively, the activating step may be omitted if, for example, the layer retains suflicent residual solvent afer having been coated on a substrate from a solution or paste to render the layer cohesvely weak.

Manifold imaging has been found to be capable of producing images of excellent quality. The imaging system, in order to achieve the optimum resolution and color separation that it is capable of producing, requires photoconductive pigment particles which are as small as possible and which preferably remain as individual species during the entire process of imaging layer formation and imaging. Moreover the commercial utilization of the process involves relatively long term storage of the imaging layer compositions thus necessitating stable imaging compositions. It would be desirable to have photosensitive pigment particles which remain as individual species during the process of imaging layer formation and imaging as well as providing imaging compositions which are stable over relatively long periods of time.

The present invention relates to a novel treatment for the photoconductive pigment particles incorporated in the imaging layer as well as the resulting photoconductive pigment particles obtained from such treatment.

SUMMARY 'OF THE INVENTION It is, therefore, an object of this invention to provide a manifold imaging system having the above-described desirable features.

It is another object of the invention to provide a treatment for photoconductive pigment particles employed in the imaging layer of the manifold imaging process.

It is still another object of the invention to provide novel photoconductive pigment part-icles for use in the imaging layers of the manifold imaging process.

It is a further object of the invention to provide imaging compositions which are stable over relatively long periods of time for use in the manifold imaging process.

The above-described and other objects and advantages are realized in accordance with the present invention by treating the electrcally photosensitive pigment particles with a polyisobutylene succinic anhydride derivative prior to incorporating the particles in an insulating binder material to form the imaging layer composition used in the manifold imaging process. The compounds used for the treatment of the electrcally photosensitive pigment particles include polyisobutenylsuccinic anhydride and reaction products of polyisobutenylsuccinic anhydride with various compounds having polar groups such as, for example, water, primary amines, secondary amines, polyhydric alcohols, inorganic metal hydroxides and the like.

The invention will be more fully understood from the following detailed description of various preferred embodments thereof particularly when read in conjunction with the accompanyng drawing wherein the Figure is a side seetional view of a typical photosensitive imaging manifold set.

Referring now to the Figure there is seen a supporting donor substrate layer 11 and an imaging layer generally designated 12. In the manufacture of the imaging member, herein referred to as the manifold set, layer 12 is preferably coated on substrate 11 so that it adheres thereto. These layers are collectively referred to as the imaging donor or merely the donor. In this particular illustrative example, layer 12 comprises photoconductive pigment particles 13 dispersed in a binder 14. Above imaging layer 12 is a third or receiving layer 16. This receiver sheet is ordinarily supplied as a separate layer which does not initially adhere to layer 12. Accordingly, although the whole imaging member or "manifold set" may be supplied in a convenient three-layer Sandwich as has been illustrated, receiving layer 16 may also be 'supplied as a separate sheet or roll if desired. On the other hand, in those systems where activation of the imaging layer is not required or where imaging layer 12 has been preactivated, layer 16 may adhere to or be tacked onto imaging layer 12. In the particular embodment of the manifold set shown in the Figure both the donor substrate 11 and the receiver sheet 16 are made up of an electrcally conductive material such as cellophane with at least one of them V being optically transparent to provide for the exposure &846,127

Zinc chloride, ferric chloride, maguesium chloride, calcium iodide, strontium bromide, chromic bromide, arsenc triiodide, magnesium bromide, stannous chloride etc.; boron halides, such as boron trifluorides; ketones such as benzophenone and anisl, mineral acids such as sulfuric acd; Organic carboxylc acids such as acetic acd and maleic acd, succinc acd, citroconic acd, sulphonic acd, such as 4-toluene sulphonic acid and mixtures thereof. In addition to the charge transfer complexes, it is to be noted that many other of the above materials may be further sensitized by the charge transfer complexing technique and that many of these materials may -be dye-sensitized to narrow, broaden or heighten their spectral response curves.

It is also to be understood in connection with the heterogeneous system, that the photoconductive particles themselves may consist of any suitable one or more of the aforementioned photoconductors, either Organic or inorganic dispersed in, in solid solution in, or copolymerized With, any suitable insulating resin whether or not the resin itself is photoconductive. This particular type of particle may be particularly desirable to facilitate dispersion of the particle to prevent undesirable reactions between the bindet 14 and the photoconductor or between the photoconductor and the activator and for similar purposes. Typical resins of this type include polyethylene, polypropylene, polyamides, polymethacrylates, polyacrylates, polyvinyl chlorides, polyvinyl acetates, polystyrene, polysiloxanes, chlorinated rubbers, polyacrylonitrile, epoxies, phenolics, hydrocarbon resins and other natural resins such as rosin derivatives as Well as mixtures and copolymers thereof.

Generally the materials used for the treatment of the electrically photosensitive pigment particles are obtained as the reaction products of polyisobutenylsuccinic anhydride with any suitable compound having polar groups.

The polyisobutenylsuccinc anhydrde used in accordance with this invention may be obtained from several commercial sources or may be prepared as below. It is suitable to use polyisobutylenes having a number average molecular weight up to about 10,000, with a preferred range being up to about 5,000.

Preparaton of Polyisobutenylsuccinic In a five liter four-necked round bottom flask place 2,000 gm. of polyisobutylene (Oronite Polybutene 24, number average molecular Weight 950, from California Chemical Co., Oronite Division), and 200 gm. maleic anhydrde. A thermometer, oil-sealed stirrer, a wide air condenser, and a gas inlet tube are attached, one to each of the flask necks, with Tefion-covered ground glass joints. A slight positive flow of dry purified nitrogen is introduced through the gas inlet tube. By use of a heating mantle the temperature of the fiask's contents is raised to 200 C. and maintained for 24 hours with stirring. Then the flask contents are allowed to cool and dissolved in three liters of cyclohexane. The contents (solution) is filtered through a Johns-Manville Celite filter-aid to remove unreacted and undissolved maleic anhydrde. The filtrate is then placed, piecemeal, in a three liter, threeneck vacuum distillation flask. The cyclohexane is distilled off at about 70 C. and then the temperature is raised slowly (with strrng) to 200 C. at about Torr to remove unreacted but dissolved maleic anhydrde and hydrocarbon "light-ends." The vscous polyisobutenylsuccinic anhydrde is cooled, poured into suitable wide mouth containers and stored until use.

Suitable polar agents which may be reacted with polyisobutenylsuccinic anhydrde to obtain derivatives of the anhydrde suitable for use in accordance with this invention are: water, primary amines, secondary amines, polyhydric alcohols, inorganic metal hydroxides and the like, which yield the corresponding acd, amide or imide, ester and metal salt of polyisobutenylsuccinic anhydrde. Usually the derivative number average molecular weight is in the range up to about 10,000 with the preferred range being up to about 5,000.

Polyisobutenylsuccinic Acd The Conversion of polyisobutenylsuccnic anhydrde to polyisobutenylsuccinic acid is accomplished by the well known method of hydrolyzing the anhydrde by the addition of water in an acidic medium. A pH of from about 1 to about 4 is the preferred acidic range.

Polyisobutenylsuccinamide Typical suitable primary or secondary amines having a primary or secondary amino group include: lower aliphatic amines such as methylamine, dimethylamine, ethylamine, dethylamine, n-propylamine, dipropylarnine, isopropylamine, diisopropylamine, allylamine, diallylamine, n-butylamine, dibutylamine, isobutylamine (Z-methylpropylamne), diisobutylamine, etc.; higher aliphatic (fatty) amines such as decylamine, dodecylamine, tetradecylamine, hexadecylamine, tetraethylene pentamine, octadecylamine, etc.; and aromatic amines such as benzylamine, fl-phenylethylamine, etc. The reaction entails simply heating and mixing a mole to mole mixture of the amine and anhydrde.

Polyisobutenylsuccinimide The Conversion of polyisobutenylsuccinic anhydrde to a polyisobutenylsuccinimide is accomplished by established aminalyss reactions, followed by heating. Generally, it is preferred to react the amines with the anhydrde during the application of heat wherein the temperature is maintained from about l C. to about 2l0 C. Although the reacting amine should contain a primary amine, the resulting polyisobutenylsuccinimide may also contain the primary, secondary or tertiary amines or mixtures thereof. A particularly preferred polyisobutenylsuccinimide results upon the reaction of polyisobutenylsuccinic anhydrde with an amine having the general formula NH -(CH -CH NH) -CH -CH -NH at about 200 C. wherein x is from 0 to 10; such as tetraethylene pentamine where x=3 above.

Ester of Polysobutenylsuccinic Acid The term polyhydric alcohol" is used heren to refet' to alcohols having two or more hydroxyl groups. Typical suitable polyhydric alcohols include, ethylene glycol; 1,2 propanediol; pentaerythritol (2,2-bis (hydroXymethyD- 1,3-propanedol); dipentaerythritol; tripentaerythritol; trimethylolethane (2 hydroxymethyl-Z-methyl-l,3-propanedol); trimethylolpropane (Z-ethyI-Z-hydroxymethyl-1,3-

propancdiol); 1,2,4-butanetriol (1,2,4-trihydroxybutane);

Metal Salt of Polylisobutenylsuccnic Acid Typical suitable inorganic metal hydroxides include the hydroxides of zinc, cadmium, lead, calcium, manganese and cobalt. Zinc and cadmium hydroxides are preferred for giving enhanced results when used in accordance with the practice of this inveution. The Conversion of polyisobutenylsuccinic anhydrde into a metal salt of polyisobutenylsuccinic acd may be accomplished by reacting the anhydrde, water and metal salt while maintaining a temperature of about l00 C. One mole of the anhydrde is 7 reacted with from 0.5 to 4.0 moles of the metal hydroxide; with 1 to 2 moles of the hydroxide preferred.

The relative proportions of the polyisobutenylsuccinic anhydride and the suitable polar agents which are to be used depend upon the product characteristics desired. For purposes of the practice of this invention, a number average molecular weight for the polyisobutenylsuccinic anhydride and its equivalents derivcd from its reacton with suitable polar agents, of up to about 10,000 is satisfactory; of up to about 5,000 being preferred. Generally, from about 20% to about 200% by weight of treating agent based on the weight of photosensitive pigment particles is employed.

Two general methods of treatment have been found effective in reducing background. Both methods involve intimate contact, such as ball milling, the photosensitive pigments with polyisobutenylsuccinic anhydride or derivatives thereof. In the first method, followed in Example I below, most of the anhydride or derivative is carried away by the vacuum filtering. Although it is not known why the practice of this invention provides the result of low background imaging, nor how the anhydride or derivatives operate within the imaging system, it is believed that small quantities of the anhydride or derivatives modify the surface of the pigments in each of the two general treatment methods.

The second general method is the same as the first except that the anhydride or derivatives are not removed from the mixture of pigment and the anhydride or derivatives and becomes incorporated in the binder matrix of the imaging layer. This results in the anhydride or derivatives being substantially uniformly dispersed in the binder of the imaging layer along with photosensitive pigments believed to have some of the anhydride or derivatives absorbed on their surfaces. This dspersion of treating agent aids in the fracture of a fracturable photoresponsive imaging layer, such as that of U.S. Pat. 3,6l5,393 hereby incorporated by reference.

As a general rule, it is preferable to use the higher portion of the previously recited 20% to 200% range by weight of treating agent (i.e., polyisobutenylsuccinic anhydride or its derivatives) based on the weight of photosensitive pigment particles, in the first treatment method above, and to use the lower portion of the range in the second treatment method just described. That is, from 20% to 110% for the second method and from 110% to 200% for the first method. This observance generally provides optimum imaging characteristics for the resulting imaging layer. However, any percentage in the range for either method improves low background imaging relative to untreated pigment particles and imaging layers.

The photosensitive pigment particles are typically treated with the polyisobutenyl succinic anhydride or its derivatives of the invention by ball milling a dispersion of the pigment in a solution of the treating agent. It is preferred to use a poor solvent for the treating agent e.g. D.C. Naphthia, so that only a small amount will go into solution. Optionally another solvent such as isopropanol or the like may be added to reduce solubility.

The binder material in the heterogeneous imaging layer or the material used in conjunction with the photoresponsive material in the homogenous layer, where applicable, may comprise any suitable cohesively Weak insulating material or materials which can be rendered cohesively Weak. Typical materials include: microcrystalline waxes such as: Sunoco 1290, Sunoco 5825, Sunoco 985, all available from Sun Oil Co. Paraint RG, available from the Moore and Munger Company; paraflin waxes such as: Sunoco 5512, Sunoco 3425, available from Sun Oil Co.; Sohio Parowax, available from Standard Oil of Ohio; waxes made from hydrogenated oils such as: Capitol City 1380 wax, available from Capitol City Products, Columbus, Ohio; Caster Wax L-2790, available from Baker Caster Oil Co.; Vitikote L-304, available from Duro commodities; polyethylenes such as: Eastman Opolene N-ll, Eastman Epolene C-12, available from Eastman Chemical Products, Polyethylene DYJT, Polyethylene DYLT, Polyethylene DYNF, Polyethylene DYDT, all available from Union Carbide; Marlex TR 822, Marlex 1478, available from Phillips Petroleum Co.; Epolene C-13, Epolene C-l0, available from Eastman Chemical Products, Polyethylene AC8, Polyethylene AC612, Polyethylene AC324, available from Allied Chemicals; modified styrenes such as: Piccotex 75, Piccotex 100, Piccotex 120, available from Pennsylvania Industrial Chemical; Vinylacetate-ethylene copolymers such as: Elvax Resin 210, Elvax Resin 310, Elvax Resn 420, available from Dupont; Vstanex MH, Vstanex L-80, available from Enjay Chemical Co.; vinyl chloridevinyl acetate copolymers such as: Vinylite VYLF, available from Union Carbide; styrene-vinyl toluene copolymers; polypropylenes; and mixtures thereof. A mixture of microcrystalline and paraflinic waxes is preferred because it is cohesively Weak and a good insulator.

As has been previously discussed the first step in the imaging process is the activation step when the latter is required. In this stage of the imaging process, the manifold set is opened and the activator is applied to imaging layer 12 following which these layers are closed back together again. The activator may be applied by any suitable technique such as with a brush, with a smooth or rough surfaced roller, by flow coating, by vapor condensation, by spraying or the like. The activator serves to swell or otherwise weaken and thereby lower the cohesive strength of imaging layer 12. The activator should preferably have a high level of resistivity to help prevent electrical breakdown of the manifold set.

Although it is preferred to use a separate electrode, sheet 16 for purposes of Simplicity is shown as a conductive receiver sheet which also acts as an electrode. Potential source 28 is connected to resistor 30, receiver sheet 16 and substrate layer 11. Au electrical field is applied across the manifold set and it is exposed to an image 2.9 to be reproduced. Upon separation of substrate 11 and receiving sheet 16, imaging layer 12 fractures along the edges of the exposed areas. Accordingly once separation is complete exposed portions of imaging layer 12 are retained on one or the other of layers 11 and 16 while unexposed portions are retained on the other layer, resulting in the formation of a high gamma positive image on one of the sheets and a high gamma negative image on the other.

The strength of the electrical potential applied across the manfold set depends on the structure of the manifold set and the materials used. For example, if highly insulating receiver and donor sheet materials are used, a much higher potential may be applied than if relatively conductive donor and receiver sheets are used. The field strength required may, however, be easily determined. If too large a potential is applied, electrical breakdown of the rnanifold set will occur allowing arcing across the manifold set. If too little potential is applied, the imaging layer will not fracture in imagewse configuration. By way of example, if a 3 mil Mylar (a polyester formed by the condensation reaction between ethylene glycol and terephthalic acid available from the E. I. du Pont de Nemours & Co., Inc.) receiver sheet and a 2 mil Mylar donor sheet are used, potentials as high as 20,000 volts may be applied between the electrodes. The preferred applied potentials across the manifold set are, however, in the range of from about 1,000 volts per mil to about 4,000 volts per mil. Since relatively high potentials 'are utilized, it is desirable to insert a resistor in the circuit to limit the flow of current. Resistors on the order of from 1 megohm to about 20,000 megohms are conventionally used.

A visible light source, an ultraviolet light source or any other suitable source of activating electromagnetc radiation may be used to expose the imaging layer of this invention. The electrically photosensitive material is chosen so as to be responsive to the wavelength of the electromagnetic radiation used. lt is to be noted that different photoresponsive materials have different spectral responses and that the spectral response of many photoresponsive materials may be modified by dye sensitization so as to either increase and narrow the spectral response of a material to a peak or to broaden it to make it more panchromatic in its response. Thus, the material can be used to make ordinary black and white" images using panchromatic response while narrow spectral response materials may be employed for the production of color separations or the like. In addition, manifold images formed on transparent materials using dierent colored imaging layers 'such as cyan, magenta and yellow may be combined to produce full natural color images by supra position. Also, either the receiver or donor sheet may be opaque providing a print on one or the other sheet.

The manifold sets may be supplied in any color desired either by taking advantage of the natural color of the photoresponsive or binder materials in the imaging layer of the manifold set or by the use of additional dyes and pigments therein whether photoresponsive or not and, of course, various combinations of these photoresponsive and non-photoresponsive colorants may be used in 'the imaging layer so as to produce the desired color.

The invention will now be described in detail with respect to specific preferred embodiments by way of EX- amples it being understood that these are intended to be illustrative only and the invention is not limited to the procedures, conditions, materials, etc. recited therein. All paris and percentages listed are by weight unless otherwise specified.

EXAMPLE I Pigments for a donor mixture are prepared as follows: 2.5 grams of Irgazin Red 2BLT pigment and 2.5 grams of Irgazin Yellow 2GLT pigment, both available from Geigy Chemical Co. and placed in a ball mill along with a solution of 1 gram of polyisobutenyl succinimide of tetraethylene pentamine in petroleum ether and ball milled for about 20 hours at a temperature of from about 60- 110 C. The resulting dispersion is vacuum filtered and then allowed to air dry.

A donor coating mixture is formulated according to the following procedure: 2 grams of x-form metal-free phthalocyanine pigment is ball milled in 50 ml. of petroleum ether at a temperature of 60-110 C. for about 20 hours. 3 grams of the aboVe-mentioned treated red and yellow pigment mixture are dispersed in 50 ml. 'of petroleum ether at a temperature of 60-ll0 C. by means of an ultrasonic probe. The two dispersions are then mixed together and 5 grams of polyethylene designated as AG-6l2 and available from Allied Chemical Co. are dissolved in the dispersion by heating to 80" C. with moderate stirring. The dispersion is then quenched rapdly by adding 700 ml. of room temperature isopropyl alcohol. The precipitated mixture is then vacuum filtered and fiushed with 200 ml. of isopropyl alcohol. The moist filter cake is redispersed in 100 ml. of isopropyl alcohol by means of an ultrasonic probe.

An approximately 25 thick coating of the donor mixture is applied to a Mylar sheet by means of a No. 22 Meyer drawdown rod and dried. After drying, the pigment binder layer is about 10 thick. The donor sheet thus formed is imaged in accordance with the manifold imaging procedure previously described. The images obtained are of moderate quality with low background on the receiver sheet and are superior to images made with no pretreatment of the red and yellow pigments.

EXAMPLE II Example I is followed except that the pgments are ball milled with 2 grams of the polyisobutenyl succinimide of tetraethylene pentamine.

10 EXAMPLE III Example I is followed except that the pigments are ball milled with 3 grams of polyisobutenylsuccnic anhydride.

EXAMPLE IV Example I is followed with the exception that the pigments are ball milled with 5 grams of polyisobutenylsuccinic acid.

EXAMPLES V AND VI Example I is followed except that the pgments are ball milled with 3 grams of the Zinc salt of polyisobutenylsuccinic acid in Example V and 3 grams of the cadmium salt of polyisobutenylsuccnic acid in Example VI.

EXAMPLE VII Example I is followed with the exception that the pigments are ball milled with 10 grams of the ethylene glycol monoester of polyisobutenylsuccnic acid (formed by reacting 1 mole of ethylene glycol with polyisobutenyl succinic acid). a

Although specific Components and proportions have been stated in the above description of preferred embodiments of the invention, other typical materials as listed above as suitable may be used with similar results. In addition, other materials may be added to the mixture to synergze, enhance, or otherwise modify the properties of the imaging layer. For example, various dyes, spectral sensitizers, or electrical sensitizers such as Lewis acids may be added to the several layers.

Other modifications and ramifications of the present invention will occur to those skilled in the art upon a reading of the present disclosure. These are intended to be included within the scope of the invention.

What is claimed is:

1. In an imaging method wherein a cohesively Weak photoresponsive imaging layer comprising electrically photosensitive partcles dispersed in an insulating binder is sandwiched between two sheets, then exposed to a pattern of actinc electromagnetic radiation and an electric field thereby providing upon separaton of the sheets a positive image on one sheet and a negative image on the other, the improvement comprising:

treating the electrically photosensitive partcles with from about 20% to about 200% by weight of said partcles of a material selected from the group consisting of polyisobutenylsuccnic anhydride and polyisobutenylsuccinc anhydride derivatives prior to formation of said images.

2. The method of claim 1 wherein said particle treatment comprises ball milling said material with said particles prior to incorporating said partcles in said photoresponsive imaging layer.

3. The method of claim 1 wherein said material is a polyisobutenylsuccnic anhydride derivative.

4. The method of claim 3 wherein said polyisobutenylsuccinic anhydride derivatives are derived by reacting polyisobutenylsuccnic anhydride with a compound having a polar group.

5. The method of claim 4 wherein said compound having a polar group is selected from the group consisting of water, polyhydric alcohols, primary amines, secondary amines, and inorganc metal hydroxides.

6. The method of claim 5 wherein said compound having a polar group is a primary amine.

7. The method of claim 6 wherein said primary amine is represented by the formula wherein x is from 1 to 10.

8. The method of claim 5 wherein said compound having a polar group is an inorganic metal hydroxide.

9. The method of claim 8 wherein said inorgam'c metal hydroxide is selected from the group consisting of the 1 1 hydroxides of Zinc, cadmium, lead, calcium, manganese and cobalt.

10. The method of claim 9 wherein said inorganic metal hydroxide is selected from the group consisting of the hydroxides of zinc and cadmium.

11. The method of claim 1 wherein the material has a number average molecular weight of up to about 10,000.

12. The method of claim 11 wherein the material has a number average molecular weight of up to about 5,000.

13. An improved fracturable photoresponsive imaging layer of the type having electrically photosenstive particles dispersed in a binder and being fracturable under the combined efl'ect of exposure to electromagnetic radiation to which the particles are sensitive and an applied electric field, wherein the improvement comprises:

a material selected from the group consisting of polyisobutenylsuccinic anhydride and polyisobutenylsuccinic anhydride derivatives substantially uniformly dispersed in said binder.

14. The method of treating electrically photosenstive materials to provide a low background maging characteristic to said materials, comprising:

intimately contacting the electrically photosenstive materials with from about 20% to about 200% by weight of said materials of a treating agent selected from the group consisting of polyisobutenylsuccinc anhydride and polyisobutenylsuccinic anhydride derivatives.

15. The method of claim 14 further including the step of removing said treating agent from intimate contact with said electrically photosenstive materials.

16. The method of claim 14 wherein the step of intimately Contacting comprises ball milling.

17. An electrically photosenstive imaging particle having the characteristic of low background imaging, comprising electrically photosenstive imaging material the surface of which has been intimately contacted with from about 20% to about 200%, by weight of said materials of a treating material selected from the group consisting wherein x is from 1 to 10.

21. The electrically photosenstive imaging particle of claim 19 wherein the polar agent is an inorganic metal hydroxide selected from the group consisting of the hydroxides of zinc, cadmium, lead, calcium, manganese and cobalt.

22.. The electrically photosenstive maging particle of claim 17 said treating material has a number average molecular Weight of up to about 10,000.

23. The electrically photosenstive imaging particle of claim 17 wherein said treating material has a number average molecular weight of up to about 5,000.

References Cited UNITED STATES PATENTS 3,615393 10/1971 Krohn 96-1 M 3,573,904 4/1971 Clark 96-1 R 3,653,889 4/1972 Luebbe 96-1 M DAVID KLEIN, Primary Examiner J. L. GOODROW, Assistant Examiner 

1. IN AN IMAGING METHOD WHEREIN A COHESIVELY WEAK PHOTORESPONSIVE IMAGING LAYER COMPRISING ELECTRICALLY PHOTOSENSITIVE PARTICLES DISPERSED IN AN INSULATING BINDER IS SANDWICHED BETWEEN TWO SHEETS, THEN EXPOSED TO A PATTERN OF ACTINIC ELECTROMAGNETIC RADIATION AND AN ELECTRIC FIELD THEREBY PROVIDING UPON SEPARATION OF THE SHEETS A POSITIVE IMAGE ON ONE SHEET AND A NEGATIVE IMAGE ON THE OTHER, THE IMPROVEMENT COMPRISING: TREATING THE ELECTRICALLY PHOTOSENSITIVE PARTICLES WITH FROM ABOUT 20% TO ABOUT 200% BY WEIGHT OF SAID PARTICLES OF A MATERIAL SELECTED FROM THE GROUP CONSISTING OF POLYISOBUTENYLSUCCINIC ANHYDRIDE AND POLYISOBUTENYLSUCCINIC ANHYDRIDE DERIVATIVES PRIOR TO FORMATION OF SAID IMAGES. 